What is the exact model of the Acer laptop?
While increasing the amount of RAM can improve overall performance a bit (because of less data caching between RAM and the hard drive), I suspect it will not help with playing back videos.
If it is a particularly old laptop, then the integrated graphics chip / core likely lacks the video codec hardware to decode modern videos properly. When this happens the video decoding is shifted from the graphics core to the CPU. Decoding modern videos (which uses the H.264 / H.265 video codecs) can be very intensive and a graphics core with the appropriate dedicated hardware decoder is much more efficient at decoding a video for proper playback compared the CPU; which would probably be pushed to working...